If you've got a huge number of images to resize regularly, it's a real pain to have to go through them individually.
Shrink O'Matic is an Adobe AIR application that allows you to take batches of images and shrink them in an instant. Shrink O'Matic handles only a limited number of formats - JPGs, GIFs and PNGs - but that should be enough for most people's needs. To shrink images, simply drag and drop them into Shrink O'Matic and they'll be resized according to the output sizes, names and formats of your choosing.
The program allows you to define the pixel length and width, compression ratio, how to name your new file, and the new format. That's it! Unfortunately, the only drawback is that there is no way to create and save profiles for shrinking images so you'll have to change the settings manually if your needs change.
However, if your main need is the batch conversion of several images at once to the same specifications, you can't really go wrong with Shrink O'Matic.
